Run non-publishing Linux builds on GitHub Actions and run with more Java versions

[wilkinsona]

Further to setting up Windows-based builds on GitHub Actions, the next step is to move our non-publishing Linux builds to GitHub Actions and also expand the Java versions that we test with. We'd like to end up with the following builds:

• Linux | Java 21
• Windows | Java 17
• Windows | Java 21

A Linux | Java 17 build will be added when we start building and publishing snapshots from GitHub Actions.